>steve/rich/marv/Tom
>
>I got the same results as Rich did, varying the current from 100ma
>to 1.2A Also tried 40ma to 800ma, and also 350ma to 3A.
>regulation was in the order of abt 14%. Got the same results
>whether using 1N5408's or using 6A10's. The 6A10's are rated at
>1kv-6A-400A surge, and are double the diam of a 5408. Same length
>and wire leads.
>
>I also tried sticking a 1000 uf - 50v rubycom electrolytic across
>the entire string. The DYNAMIC reg was then WAY less than 14%
>on ssb/cw.
>
>6A @ .8V = 4.8 Watts. Hot as hell if CCS.
>
** Yeah, but how many guys run a 3cx10,000A7/8160. However, with the
airflow required to cool one of those suckers, the cathode bias diodes
would run way cooler. [an 8160 with 10kV DC on the anode drives quite
nicely with a pair of 3-500Zs]
>I use 10 x 1N5408's with a 1000 uf 50V lytic in all my 3 x
>L4B's. The drake L4B ran zero bias (240ma idle on ssb
>position-2600V) This mod dropped the idle down to 100Ma on ssb,
>and 40Ma on CW(1900V) I used a 3 position center off toggle,
>spdt-center off to give me 3 positions of bias.
>
** 150mA of ZSAC is mo' betta for 2, 3-500Zs on SSB.
>Funny, with 40ma of idle on 1900v cw position, zero imd results,
**There is never, ever any imd on CW.
>as measured 1/2 mile away on ssb. Drive requirements went up by
>6-8 watts.
>
>Also tried grounding with some strap, just ONE grid pin of each
>3-500Z. Drive requirements dropped on all bands by 20 watts.
>Drake had used 3 x 200pf caps + 1 choke on each tube socket.
>Heath later copied same ckt. I mentioned this to my buddies
>with TL-922's + SB-220/ SB-221's.
>
** 3, 200pF caps to bypass a 3-500Z grid is not enough below c. 20MHz.
>1800pF is better. // I wonder what Bill Orr was thinking when he came up
with the idea of a 600pF grid-bypass? Maybe he wasn't?
>They also tried the grounding just one grid pin of each socket
>and all reported the same 20w reducrion in drive power. The
>fellows with the SB-221's also reported that their output power on
>10M shot up from 700-800 watts to 1350-1400 !!
>
>The fellows with the TL-922's reported that they could now remove
>the AG6K nichrome suppressors, and the TL-922's were now rock
>stable.
>
>On the big metal triodes,
** The 3cx1000A7 perhaps?
> I use a 12 position rotary switch and
>50 x 6A10's + 1 lytic across the entire mess. I tap right after
>diode #10, then every 3rd diode after that.
>
>Question is, what is the optimum value of the electrolytic to be
>used across the entire string ???
** A 1F electrolytic makes virtually zero difference since the bias V
moves little with no cap..
> I have only tried just the
>1000uf - 50V unit.
>
>Would 10,000 uf buy me anything ??
** bragging rights to use on 11m only?
> I'm wondering about the
>esr/temp rating/capacitance value/voltage rating/current rating of the
>ideal cap to be used.
>
>A string of either 5408's or 6A10's are bullet proof. These
>days I just buy 6A10's by the bucket load. I use em in the
>HV supplies and also meter protection ckts etc. 2-3 in parallel,
>all pointed same way, between chassis and B- ensures no
>surprises.
>
>You can post any or all of this note if you like. Looking
>forward to any comments or suggestions.
>
>Thanks fellows
>
>Jim Thomson VE7RF
>
great call, Jim
- R. L. Measures, a.k.a. Rich..., 805.386.3734,AG6K,
www.vcnet.com/measures.
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